Jan 30, 2012

K & R C Programs Exercise 5-10.

K and R C, Solution to Exercise 5-10:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
C Program to evaluate reverse Polish expression from the command line, where each operator or operand is a separate argument.
For example:expr 2 3 4 + * evaluates 2 X (3 + 4). Read more about C Programming Language .

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#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>

#define MAX 1000

double stack[MAX];
int stack_height = 0;

void panic(const char *msg) {
	fprintf(stderr, "%s\n", msg);

void push(double value) {
	if (stack_height == MAX)
		panic("stack is too high!");
	stack[stack_height] = value;

double pop(void) {
	if (stack_height == 0)
		panic("stack is empty!");
	return stack[--stack_height];

int main(int argc, char **argv) {
	int i;
	double value;

	for (i = 1; i < argc; ++i) {
		switch (argv[i][0]) {
		case '\0':
			panic("empty command line argument");
		case '0':
		case '1':
		case '2':
		case '3':
		case '4':
		case '5':
		case '6':
		case '7':
		case '8':
		case '9':
		case '+':
			push(pop() + pop());
		case '-':
			value = pop();
			push(pop() - value);
		case '*':
			push(pop() * pop());
		case '/':
			value = pop();
			push(pop() / value);
			panic("unknown operator");

	printf("%g\n", pop());
	return 0;

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